12.5.1 Where steering and/or stabilization of
a craft is essentially dependent on one device, as with a single rudder
or pylon, which is itself dependent on the continuous availability
of electric power, it shall be served by at least two independent
circuits, one of which shall be fed either from the emergency source
of electric power or from an independent power source located in such
a position as to be unaffected by fire or flooding affecting the main
source of power. Failure of either supply shall not cause any risk
to the craft or passengers during switching to the alternative supply
and such switching arrangements shall meet the requirements in 5.2.6. These circuits shall be provided
with short-circuit protection and an overload alarm.
12.5.2 Protection against excess current may be
provided, in which case it shall be for not less than twice the full
load current of the motor or circuit so protected and shall be arranged
to accept the appropriate starting current with a reasonable margin.
Where three-phase supply is used, an alarm shall be provided in a
readily observed position in the craft's operating compartment that
will indicate failure of any one of the phases.
12.5.3 Where such systems are not essentially
dependent on the continuous availability of electric power but at
least one alternative system, not dependent on the electric supply,
is installed, then the electrically powered or controlled system may
be fed by a single circuit protected in accordance with 12.5.2.
12.5.4 The requirements of chapters
5 and 16 for power supply of
the directional control system and stabilising system of the craft
shall be met.